Can someone please help me with some steps towards solving this problem?

A glass tumbler containing 243.3cubic centimeters of air at 1.00e2kPa (barometric pressure) and 20Celsius is turned upsde down and immerse in a body of water to a depth o 20.5m. The air in the glass is compressed by the weight of water above it. Calculate the volume of air in the glass, assuming the temperature and barometric pressure have not changed. (80.7cubic centimeters)